Rain, wind expected all week; flooding possible

WEATHER

Tom Abate, Chronicle Staff Writer

Published
4:00 am PST, Monday, January 18, 2010

People in line at Powell and Market streets for the cable car huddle beneath their umbrellas during a brief downpour. The predicted storms for the week began Sunday, but rainfall was sporadic in downtown San Francisco during the afternoon. less

People in line at Powell and Market streets for the cable car huddle beneath their umbrellas during a brief downpour. The predicted storms for the week began Sunday, but rainfall was sporadic in downtown San ... more

Photo: Brant Ward, The Chronicle

Photo: Brant Ward, The Chronicle

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People in line at Powell and Market streets for the cable car huddle beneath their umbrellas during a brief downpour. The predicted storms for the week began Sunday, but rainfall was sporadic in downtown San Francisco during the afternoon. less

People in line at Powell and Market streets for the cable car huddle beneath their umbrellas during a brief downpour. The predicted storms for the week began Sunday, but rainfall was sporadic in downtown San ... more

Photo: Brant Ward, The Chronicle

Rain, wind expected all week; flooding possible

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The Bay Area is in for one of its wettest weeks, with a series of windy storms expected to drop 8 inches of rain on San Francisco, soak higher elevations even more, and create the potential for power outages and floods.

The dark clouds, though, may have a thick silver lining: Meteorologists expect 5 to 7 feet of powder in the Sierra Nevada, enough to bring the snowpack up to 100 percent of normal for this time of year.

That, in turn, may help to replenish California's reservoirs next spring and ease the effects of a three-year drought.

Forecaster Bob Benjamin of the National Weather Service said the unusual series of storms, accompanied by gale-force winds, is expected to peak in intensity Wednesday and taper off on Friday and Saturday. The sun could emerge for a while before yet another drenching next Sunday and Monday.

"I don't think there is any period for the next several days when we will have a dry spot," Benjamin said.

A Weather Service wind advisory says the storms could bring gusts of 25 to 35 mph or more, making driving difficult for high-profile vehicles and potentially knocking down tree limbs or power lines. Pacific Gas and Electric has crews standing by to deal with possible power outages but is not ringing any alarms.

Flooding possible today

The Weather Service also warns that the rain will be falling so fast today that flooding of local roadways and low-lying areas is possible.

Benjamin said the downpour is expected to increase in volume around Wednesday. At that point, the ground could be sufficiently soaked by prior rains to make flood-prone streams and rivers susceptible to overflowing.

"We're just watching to see how it develops," Foot said. "If we're going to have problems, it will be Wednesday."

In Napa, which flooded most recently four years ago, city officials started offering sandbags to residents on Saturday and held a meeting on Sunday to get their disaster-preparedness officials in touch with Weather Service experts.

"The Napa Creek floods when we get more than 3 inches in 12 hours, and there is the potential on Wednesday for us to get that," said Dan Hall, battalion chief with the city's fire department.

What makes the coming storms unusual, said Benjamin at the Weather Service, is that they are coming straight across the Pacific Ocean, rather than following more typical southern or northern trajectories that would bring warmer or colder rains, respectively. He said these mid-Pacific storms will keep temperatures in coastal regions between lows in the 40s and highs in the 50s.

"Moist and cool, that is the picture for the week," he said.

In the higher, colder elevations of the Sierra, the coming storms are likely to dump enough white precipitation to bring the snowpack - now 65 to 70 percent of average - up to or above its seasonal reading, said Rhett Milne, a National Weather Service meteorologist in Reno.

Boon for skiers - but not travelers

Milne said the snow will be a boon for ski resorts as well as for California's drought-parched reservoirs. But travel to and from regions like Lake Tahoe will be fraught with delay and peril as the high winds and nonstop storms create blizzard and whiteout conditions at various times.

Sunday's initial flurries had drivers putting on chains on Highway 50 and Interstate 80, where afternoon traffic was creeping at under 20 mph on a long stretch heading west from Donner Summit.

Meanwhile, Southern California authorities fear the coming storms could trigger debris slides in suburban communities northeast of Los Angeles, where last year's Station Fire denuded hillsides of trees and shrubs that might have absorbed the rains.

Storm glance

What's the forecast? Rain is expected throughout the week. Storms are expected to peak on Wednesday, tapering off on Friday and Saturday.

How much could fall? Nine inches of rain is expected in San Francisco, with more in higher elevations. The Sierra could see 5 to 7 feet of snow.

What could it mean? The snowpack could reach 100 percent of normal for this time of year.